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Abstract: We report on new retrievals of water vapor column abundances from the Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) data. The new retrievals are from the TES nadir data taken above the ‘cold’ surface areas in the North polar region (T surf <220K, including seasonal frost and permanent ice cap) during spring and summer seasons, where retrievals were not performed initially. Retrievals are possible (with some modifications to the original algorithm) over cold surfaces overlaid by sufficiently warm atmosphere. The retrieved water vapor column abundances are compared to the column abundances observed by other spacecrafts in the Northern polar region during spring and summer and good agreement is found. We detect an annulus of water vapor growing above the edge of the retreating seasonal cap during spring. The formation of the vapor annulus is consistent with the previously proposed mechanism for water cycling in the polar region, according to which vapor released by frost sublimation during spring re-condenses on the retreating seasonal CO2 cap. The source of the vapor in the vapor annulus, according to this model, is the water frost on the surface of the CO2 at the retreating edge of the cap and the frost on the ground that is exposed by the retreating cap. Small contribution from regolith sources is possible too, but cannot be quantified based on the TES vapor data alone. Water vapor annulus exhibits interannual variability, which we attribute to variations in the atmospheric temperature. We propose that during spring and summer the water ice sublimation is retarded by high relative humidity of the local atmosphere, and that higher atmospheric temperatures lead to higher vapor column abundances by increasing the water holding capacity of the atmosphere. Since the atmospheric temperatures are strongly influenced by the atmospheric dust content, local dust storms may be controlling the release of vapor into the polar atmosphere. Water vapor abundances above the residual polar cap also exhibit noticeable interannual variability. In some years abundances above the cap are lower than the abundances outside of the cap, consistent with previous observations, while in the other years the abundances above the cap are higher or similar to abundances outside of the cap. We speculate that the differences may be due to weaker off-cap transport in the latter case, keeping more vapor closer to the source at the surface of the residual cap. Despite the large observed variability in water vapor column abundances in the Northern polar region during spring and summer, the latitudinal distribution of the vapor mass in the atmosphere is very similar during the summer season. If the variability in vapor abundances is caused by the variability of vapor sources across the residual cap then this would mean that they annually contribute relatively little vapor mass to significantly affect the vapor mass budget. Alternatively this may suggest that the vapor variability is caused by the variability of the polar atmospheric circulation. The new water vapor retrievals should be useful in tuning the Global Circulation Models of the martian water cycle. [Copyright &y& Elsevier]

In situ measurements of how air temperature near the surface responds to changing topography on other planets are rare. The Bagnold dunes were investigated by Mars Science Laboratory's Curiosity rover during its second winter in Gale crater on Mars. The effect of Bagnold dune slopes on the local microclimate air temperature, potential temperature, near‐surface lapse rate, and how they change the variability of short‐lived air temperature fluctuations is described. The oscillations with periods under 24 min are characterized using Fourier analysis. Comparing the sols during the Bagnold dunes exploration to a typical southern winter sol, we characterize the changes in temperature oscillations near the east facing High dune, the west facing Namib dune, as well as in the area between the dunes. Each of the regions had distinct signatures, with the west and east orientation of the dunes affecting the data. Plain Language Summary: This manuscript describes the first in situ measurement of the observed effect of terrain slopes on the near‐surface air temperatures of another planet: (a) Air temperatures fluctuated due to convective activity and downslope topographic flows. (b) Both phenomena caused oscillations with different frequencies. (c) The proximity to dunes slopes changed the times of transition from stable to convective atmosphere depending on the orientation of the slopes. The proximity to a steep west face of Namib dune induced rapid oscillations during the evening downslope flow. Key Points: Frequency regimes for convective versus topographic air temperature oscillations are found at Gale crater's surface layerUnique air temperature and inversion dynamics on Sols 1222‐1239 were caused by local slopes at the Namib duneAir temperature oscillation frequencies and regime transitions from neutral to convective are modulated by slopes grade and orientation [ABSTRACT FROM AUTHOR]

Diurnal and annual water cycles are studied during the first year of Perseverance rover in Jezero, using observations from the Mars Environmental Dynamics Analyzer (MEDA) and column modeling. Areal values for the ground thermal inertia (TI) and albedo are first found at one site by fitting model temperatures to the observed air temperatures. Areal soil porosity and the initial water vapor volume mixing ratios (vmr) are next found via model-vmr fits to the observation-based vmr. The meteorology and physics of the modeled air and subsurface diurnal moisture cycle at the site is then discussed in detail. The process of fit to observations is finally extended to fourteen sites along the Perseverance track, resulting in estimates for areal TI, albedo and porosity at these sites, and in MEDA-based initial estimates for the annual and diurnal moisture cycles at Jezero during MY36. • MEDA diurnal observations and column model are compared at 14 sites in Jezero. • Fits to MEDA air temperatures provide model values for areal TI and albedo. • Fits to MEDA air moistures provide model values for areal porosity and column water. • Meteorology and physics of the diurnal moisture cycle is described in detail. • Annual site-by-site results appear to agree with satellite retrievals. [ABSTRACT FROM AUTHOR]

The diurnal water cycle was studied at a Jezero crater base site using M2020 observations and adsorptive column modeling in a cool midwinter period just before a dust peak and at the peak. During low-dust sols 566–571 the observed air relative humidity (RH) at 1.45 m height was high, 40–90% near dawn. For the typical nocturnal wind speed of 2 m/s at 1.45 m and column water of 9.7 μm, the model's diurnal air temperatures and RH were within observations. For weaker winds model-RH increased as in some of the observed sols. In a nearly calm experiment fog formed from 1.45 m upward. Ground frost appeared independently of wind, but only if adsorption was disabled. The dust peak at around sol 577 was also well simulated with the same wind and absolute humidity as before the event, but relative humidities dropped dramatically due to the dust-enhanced higher nocturnal temperatures. • MEDA midwinter observations and column model results are compared. • Model match is good in a high-RH low-dust period for typical winds. • Model indicates radiation fog near dawn during very weak winds. • Frost is formed only without adsorption to ground, regardless of wind. • RH decreases in the dust event due to increased nocturnal temperatures. [ABSTRACT FROM AUTHOR]